armybikerider

I've got a 12 speed Campy SR drivetrain with approximately 21,500 miles on it. 2 days ago the rear derailleur started making a sound like there was a stiff link in the chain. That sort of "clunk" without shifting gears. But the sound is irregular and seemingly random. The sound is not reproduced with increased pedal pressure, happens on multiple cogs and chainring combinations, is not consistent and is totally random as far as I can tell. The chain (the 4th on this bike) measures exactly 12 inches with my metal ruler and is clean and lubed......there isn't excessive wear on the cogs or chainwheel as far as I can tell, and I've cleaned and lubed all the pivot points on the derailleur. Oh and the shifting is fine in both directions.


I thought the chain might be the issue but after measuring I'm not so sure. Might be the cassette but all the cogs looked good to me. Maybe the B tension screw? Maybe I should replace the chain despite what I measured?


Any other ideas?

Andrew R Stewart 

Stiff links should be fairly easy to find. Relax the chain tension and use your fingers to flex the chain links both ways as you feed the chain through your fingers. The key is no tension.

Sometimes links can become damaged so that a burr or other "feature" can develop. Again running the chain through one's fingers can expose this.

But given the description and all I wonder if the freehub body ratchet is the root. Has this been service since new? Andy

ScottCommutes

I would go ahead and try a new chain on the simple logic that it's easy to swap chains and it's good to have an extra one on hand anyway. If that fixes it, pitch the old chain.

While you're at it, check the guide pulley on the derailleur. You have a lot of miles on that derailleur. See if there is play in the guide pulley that is starting to let the chain occasionally slap against an adjacent gear.

FBinNY 

It could be a stiff link, which like a medical issue, likes to hide when a pro is looking. So, I look for these by backpedalling in a aligned gear combination while pushing forward on the lower cage enough to ease lower loop tension. Then I look for a link that doesn't straighten as it spools off the idler pulley.

That said, there may be another answer, especially if the "clunks" tend to happen under load.

This is a new chain, and at 21,000 miles it's fair to guess that the cassette is pretty worn, despite you not seeing it. That combination is strong possibility as the cause of the issue. This is hard to test for conclusively, but one thing I do I'd shift to a commonly used gear. Then use an ice pick to lift the chain off the sprocket at about 9 o'clock or so. If the chain lifts significantly, pulling links from either side, the sprocket is worn.

Confirm by borrowing a newer one fom a friend or other wheel. Or, since you'll need one soon enough anyway, buy it now and see. If that solves it, you're done, otherwise, put the old one back and look for another problem.

ScottCommutes

Also, 21,500 miles is a good run for a drivetrain. I wouldn't feel bad about replacing everything mentioned and then some. Even if the parts have some life left in them, they are getting long in the tooth.

Kontact

Take a look at the pulleys.

Duragrouch

I got a great mountain bike cheap at a garage sale, skipped, close examination of chain showed one link that looked like it had been bashed while hitting a concrete step, removed, bike worked perfect.

Second, inspect all links for any cracks, should be easy to see.

I also agree with new chain skipping on old cogs, happened to me, and since that meant the cogs were too far gone to prevent with a new chain, I put the old chain back on until I am ready to replace cogs too. Which I haven't done because the wheels are long in the tooth, sidewalls concave, I think I'll just grab both wheels with like-new cassette from a similar folder I picked up a few years ago and have not yet rehabbed, neglected but wheels and cassette in fine shape.

mpetry912 

the thing about 12 speed - that is different than a 6 speed garage sale bike - is that every part of the drivetrain has to be in very good condition.

percieved performance - be it reliable shifting, overall smoothness under load, etc - will deteriorate pretty rapidly with any wear

these high end drivetrains are not tolerant of worn or damaged parts.

I'd look carefully at the chain, really eyeball it, looking for a link where the pin is loose or binding

or, just replace the cassette, pulleys, and maybe chainrings

/markp

grumpus

Sticky cable?

rm -rf

I'm not sure what this means: "The sound is not reproduced with increased pedal pressure".
Is it:
1. Just as random when doing hard pedaling efforts.
2. Doesn't happen with hard efforts, only with easier pedaling force.
3. something else?

armybikerider

Yes the sound is random regardless of pedaling efforts. Happens with hard or easy efforts.

I ordered a chain today. I'll start there and see what happens.

FBinNY 

Fixing a bike isn't like throwing spaghetti against the wall to see if it sticks.

You have to form a theory, then test to confirm. I earlier suggested a test for worn sprockets. Do that before moving on.

The B screw is a possibility but only likely if you changed the chain length. In any case, use you eyes. There should be 1/2" of free chain between leaving the pulley and joining the sprocket. However, B screw issues usually only manifest on one or two gear combinations.

So, follow a step by step process until you score.

ScottCommutes

Do they call this "parts cannon" in bike repair? I'm only familiar with the term in the context of auto repair.

It's never the best way to fix anything, but in certain situations even missing with the cannon (replacing parts that aren't the problem and have some life left in them) isn't a bad thing if you save the diagnostic time and end up with replacement parts installed that will be good for many thousands of miles more than what you started with.

If I recall correctly, 50% of automotive starters and alternators that are exchanged for rebuilds turn out to function correctly. Lots of pros are evidently throwing parts at cars to see what sticks. For bad and sometimes good, the practice is widespread.

grumpus

Sounds like they failed to check voltage drop on the connectors before condemning the parts, I wonder if simply removing/replacing the "bad" parts would have had the same effect as fitting new. It seems many "mechanics" are sorely lacking in diagnostic skills, and should stick to doing oil changes. Having said that, it's next to impossible to diagnose some bike noises ...

KerryIrons

Really? My current Campy Chorus drive train has 86,000 miles on it. I replaced one of the chain rings at 65,000 miles. Other than that just chains and cassettes when they wear out. No way should Campy drive train be worn out at that mileage unless it gets ridden in the rain a LOT.

FBinNY 

+1

We need to be more discerning when talking about "drivetrain" wear.

Obviously chains, and to a slightly lesser extent, cassettes wear fairly quickly. But that's pretty much where it ends.

Of course, other parts will need replacing now and then, but otherwise, 21,000 miles isn't a lot.

armybikerider

Thanks for all the suggestions. I appreciate the input. And for the record I do not ride in the rain or even on wet roads.

My initial theory was a stiff link. I've confirmed that it is not. The chain actually is not new. As stated it's the 4th chain on this bike since new. It's got approximately 4,000 miles on it which is the lowest of all previous chains on this bike and is a Chorus chain btw. I tried the test you mentioned for worn sprockets but it was negative. Again, the "clunk" doesn't necessarily happen with heavy pressure on the pedals. It's random.
I'm operating on the theory that the chain is the culprit - regardless what I measured, and ordered a new one last night. I need one anyway as a spare and if a new chain proves the cure even better. If not the cassette will be replaced. I really dont think the derailleur is at fault.

Kontact

How did the pulleys look when you checked those?

armybikerider

The pulleys spun smooth with no side-to-side play or slop.

Thanks

choddo

Dumb suggestion just because it happened to me yesterday and I thought of this thread: it’s not that thing where you shift and have a little slack in the crank/chain and the pedals sort of take a bit of rotation to re-engage the freehub?

armybikerider

No dumb suggestions. I welcome all ideas. But no, the problem I have is not the same.

alcjphil

I had a similar problem a couple of years ago. It turned out that one of the outer side plates of the chain was starting to separate outwards. New chain fixed the problem. It was so slight that you couldn't even see it. The chain would probably have broken If I hadn't changed it
Found the problem on my workstand. When the chain was on the smallest cog, the chain would rub on the dropout just once per revolution of the chain.

armybikerider

Update and resolution.

I installed a new chain today and the drivetrain is once again silent. i checked the old chain closely and there was no stiff link or any abnormality that I could see or feel. It did measure about 1/16 longer than the new chain. BTW the new chain is SRAM Force flat top.

Kontact

I'm surprised it isn't too little for the Campy teeth.

armybikerider

The Force chain works perfectly with Campagnolo SR 12 speed. This is the 5th chain on this bike and the 2nd Force chain in 21000 + miles.